I need help

I have been with my boyfriend for the last 6 years. The first three years were truly a challenge, the first two I dealt with him talking to different girls, trying to flirt and get with them from time to time and constantly argued with him about it. The third year he actually chose to watch me leave instead of cutting off communication with one girl in particular. In the end her baby father came and found my at the time "ex-boyfriend" and ended up mashing up his car.. guess she wasn't the single woman she claimed to be in the end. During this time I confided in a guy friend I had known long before I met my boyfriend and ended up having sex with him, thinking it would make me feel better. Boy was I wrong. I felt terrible about it and I didn't tell my boyfriend.
Time passed and eventually my boyfriend begged me to allow him back and I gave in. At the end of the day I love him. But, I always felt at the back of my mind that I needed to keep my guard up, I told him I had forgiven him because I thought I did. 
Turns out I didn't and I realized how angry I was after spending the rest of the third year and almost all of the fourth and fifth year dealing with constant arguments, because of HIM accusing me of doing wrong, him not trusting me. 
Late fifth year and early sixth year I started talking to my old friend and other guys, and spent a lot more time on my phone than usual because I guess I stopped feeling loved. 
My boyfriend decided to go through my phone and found everything, and broke my phone. Immediately I felt regret, I felt so sorry about what I had been doing and for the past month I have been trying. I have not replaced my phone, I have had no communication with anyone. 
Recently he told me that my efforts are not enough and the only choice I have to make him consider staying with me is to engage in a threesome. This is something I am not into, I am turned off by the idea and repulsed that he would degrade me in such a way. 
Am I wrong for choosing not to do this? Am I wrong for saying I would do anything and then turning around and declining the threesome? Please help..